1. Field of the Invention
The present invention relates to the production of hydrogen from waste materials. In particular, the present invention is directed to a process of using anaerobic fermentation to maximize the production of hydrogen from waste materials.
2. Description of the Related Technology
Hydrogen is an important feedstock in industrial processes as well as a potential source of clean energy either by combustion or use in fuel cells. Hydrogen has the highest energy content per unit weight of any known fuel and can easily be converted to electric energy via fuel cell technology. In addition, hydrogen generates only water when combusted and therefore provides an environmentally-friendly option for energy generation. Therefore, hydrogen has been described as the fuel of the future (Serfass et al., “Practical hydrogen development strategy,” International Journal of Hydrogen Energy, vol. 16, pages 551-556, 1991). Currently, more than 90% of commercial hydrogen is produced by steam reforming. In steam reforming, high temperature water/steam is reacted with hydrocarbons such as natural gas, thereby producing hydrogen and carbon dioxide. However this process uses fossil fuels as starting materials and thus is an energy intensive process.
Fermentation processes using microorganisms provide an environmentally friendly alternative means for hydrogen production. One drawback of this alternative is the low yield and its susceptibility to end-product inhibition of hydrogen production (Taguchi et al., “Hydrogen production from continuous fermentation of xylose during growth of Clostridium sp. strain No. 2,” Can. J. Microbiol., vol. 41, pages 536-540, 1995). This drawback makes this alternative uneconomical for commercial production of hydrogen. In addition, light is required in many of these fermentation processes, which makes large scale fermentation impractical in some circumstances.
It has also been proposed that anaerobic fermentation may be a practical alternative for hydrogen production because of its advantages such as its high yield of hydrogen, no requirement for light energy, and because this process is capable of using organic waste materials to provide nutrients for the microorganisms (Hawkes et al., “Sustainable fermentative hydrogen production: challenges for process optimization,” Int. J. Hydrogen Energ., vol. 27, pages 1339-1347, 2002).
U.S. Pat. No. 7,901,916 teaches a method for producing hydrogen by a batch fermentation process from pretreated organic waste as a substrate for microorganisms. The process comprises pretreating an organic waste and fermenting the pretreated organic waste under anaerobic conditions and with an initial pH of 7 to 9. This anaerobic fermentation process is operated in batch mode. The organic waste may be food waste, sewage sludge or livestock waste water. Pretreatment of the organic waste may be by heat treatment, an acid treatment, an alkali treatment or any combination thereof.
U.S. Pat. No. 8,501,463 discloses a method for producing chemicals by anaerobically fermenting biomass using anaerobic bacteria. The chemicals that may be produced include hydrogen gas, volatile organic acids, solvents, solids, and salts of volatile organic acids. The biomass may be pretreated before the anaerobic fermentation step by one or more pretreatment techniques that include sterilization, deoxygenation, concentration, detoxificatipn, and/or pre-digestion. The biomass may be energy crops, surplus agricultural products, waste from sugar production and processing facilities, waste from fruit processing industries, waste from pulp and paper mills, silvaculture residues, waste from wood processing, waste from agricultural product processing, food waste, solids isolated from fermentation cultures, municipal sewage waste, animal manure, animal urine, and animal parts.
Parkin et al. (“Fundamentals of anaerobic digestion of wastewater sludges,” Journal of Environmental Engineering, vol. 112, pages 867-920, 1986) provides a comprehensive discussion of anaerobic fermentation of municipal wastewater sludges to produce methane and hydrogen. The anaerobic fermentation process may be optimized by adjusting retention time, mixing conditions to maximize bacteria-substrate contact, pH and temperature, the type and amount of nutrients, removal of toxic materials, and feed ratios.
Oh et al. (“The Relative Effectiveness of pH Control and Heat Treatment for Enhancing Biohydrogen Gas Production,” Environ. Sci. Technol., vol. 37, pages 5186-5190, 2003) discloses a method for hydrogen production by fermentation of organic substrates at high concentrations while suppressing hydrogen transfer to methanogens by heat treatment, removing non-sporeforming methanogens from the inoculum, and lowering the pH of the fermentation process. It was found that low pH was, without the heat treatment, sufficient to prevent hydrogen losses to methanogens in a mixed batch fermentation.
Chong et al. (“Biohydrogen production from biomass and industrial wastes by dark fermentation,” International Journal of Hydrogen Energy, vol. 34, pages 3277-3287, 2009) discloses a method for hydrogen production by dark fermentation of biomass. Suitable biomass for hydrogen production includes food and starch-based wastes, cellulosic materials, dairy wastes, palm oil mill effluent and glycerol. Hydrogen production is said to be enhanced by lowering hydrogen partial pressure during anaerobic biodegradation, possibly accompanied by pH control, CO2 removal and pretreatment of the biomass. The hydrogen partial pressure may be lowered by either stripping with an inert gas or vigorous agitation of the fermentation medium.
U.S. Pat. No. 5,705,374 teaches a process for producing hydrogen and carbon dioxide from an anaerobic culture medium using a proteobacteria. The preferred proteobacteria is Desulfovibrio sp. ATCC 55738 (FOX1). The culture medium includes a carbon source selected from formic acid, a formate and mixtures thereof, a nitrogen source and vitamins.
US 2007/0207531 discloses a method for producing hydrogen by fermenting a culture medium containing sugar. The fermentation is maintained under substantially anaerobic conditions and employs a bacterium of the genus Clostridium, preferably Clostridium bifermentans. The disclosed method can produce hydrogen with an efficiency of at least about 34% relative to the maximum theoretical yield.
The present invention provides a method of hydrogen production through anaerobic fermentation of waste materials. The method removes hydrogen during the anaerobic fermentation, thereby reducing suppression of hydrogen production by the produced hydrogen. The method is capable of enhancing the yield and/or selectivity of hydrogen production.